Collection of airborne material by electrostatic precipitation



w. A. PERKINS ETAL 2,868,318 COLLECTION OF AIRBORNE MATERIAL BY ELECTROSTATIC PRECIPITATION Filed June 23, 1955 Jan. 13, 1959 Yr m w m m mmaw m V1 0 w. AW. d 7 mam lf/f/ll/ll w 2.2032 N\ vN W v 1 V\ p- .ww /M .WHHHJ JW All W 1 mwww F 1 .i {EMF 9 i i Ii I United States Patent COLLECTION OF AIRBORNE MATERIAL BY ELECTROSTATIC PRECIPITATION William A. Perkins, Los Altos, Stuart W. Griunell, Menlo Park, and Conrad F. Schadt, Palo Alto, Calif assignors to the United States of America as represented by the Secretary of the Army Application June 23, 1955, Serial No. 517,664

3 Claims. 01. 183-7) This invention relates to a method of collecting airborne particulate material from a current of air. More particularly, it relates to a device and a method of allowing a current of air to impinge on an anode surface whereby the particles in the air are made to adhere to the anode and can thereafter be examined under a microscope.

In the drawings, Fig. 1 shows a longitudinal section of the precipitator and Figs. 2 and 3 show transverse sections at 2-2 and 3-3 respectively. More particularly, 2 is a transparent tube preferably made of a plastic material such as Lucite. Each end of the tube 2 is fitted with stoppers 4 and 6 which have openings 8, 10 and 12. Opening 8 in stopper 4 receives a smaller Lucite tube 14 within which is a perforated spacer 16 supporting a Bakelite rod 18. This latter rod is the insulator for the cathode 20. In stopper 6 there are two openings, 10 and 12. The latter opening is centrally located and supports the anode rod 22. Anode disk 24 is fastened to the end of this rod perpendicular to it and the cathode. Opening 10 serves as an exit for the air which enters through tube 14. An electrical circuit is completed through a 10 megohm resistor in series with the cathode which assists in maintaining a corona discharge at the cathode.

In operation, air is drawn inthrough tube 14, around anode 24 and out opening 10. A potential of 8,000 to 10,000 volts is maintained between anode and cathode which produces a corona discharge at the cathode. Particulate matter in the air entering through tube 14 impinges on the anode disc 24 and adheres thereto over an area substantially equal to the cross sectional area of tube 14. The volume of air passing through the instrument can be determined by time and velocity of flow and the particulate matter therein which has collected on the anode can be examined under a microscope to determine amount as well as size of particles.

As a practical embodiment, the Lucite tube may be about 2%" internal diameter with a length of 6" and with other dimensions in proportion. With such a tube, having a cathode-anode spacing of 6 mm. and a voltage of 8,000 to 10,000, it was possible to maintain an air flow of 100 liters/min. with a small blower using about 10 watts. With such a rate of flow, at least of all particulate matter in the air is collected, even where the particle size is only but 1 to 5 microns in diameter.

The anode surface is highly polished thereby making it possible to clearly see the nature and amount of the particulate matter under a microscope, using surface illumination.

Several modifications of the instrument: are possible. Thus, several cathodes may be installed around the one anode and the air may be sampled through any one or all of the cathodes and deposited on different. areas. Conversely, the anode surface may be rotated thereby placing new surface areas in front of the cathode. Due to the transparent outer tube of the instrument, it is possible to observe the anode surface at all times thereby preventing an excess of anode deposit to be built up before examination is made.

We claim:

1. An electrostatic precipitator comprising a longitudinal tube having an anode surface therein perpendicular to and supported by a central shaft coincident with the axis of said tube, a pointed cathode supported normally and in close spacing to said anode surface and to one side of the center thereof including means to admit air around said anode in a stream confined to a small area of said anode and including electrical means to supply a direct current potential difference of 8,000 to 10,000 volts between cathode and anode.

2. An electrostatic precipitator in accordance with claim 1 wherein the anode supporting shaft is positioned in a stopper in the end of the tube, said stopper containing an additional opening for exhausting air from the tube.

3. An electrostatic precipitator in accordance with claim 1 wherein the anode surface is highly polished and is rotatable to expose new surfaces to the cathode discharge.

References Cited in the file of this patent UNITED STATES PATENTS 1,069,993 Amos Aug. 12, 1913 1,992,113 Anderson Feb. 19, 1935 2,244,278 White June 3, 1941 2,748,887 Osmar June 5, 1956 OTHER REFERENCES Perry: Chemical Engineers Handbook, 3rd ed., Mc- Graw-Hill (1950), pages 1039-1045. 

